1. Field of the Invention
The present invention relates to an apparatus for drying laundry, and more particularly to a method for controlling such a laundry drying apparatus, capable of controlling the output of a heater unit of the apparatus, based on the amount of laundry to be dried.
2. Description of the Prior Art
Referring to FIG. 1, there is illustrated a conventional apparatus for drying clothing. As shown in FIG. 1, the apparatus comprises a motor 1 disposed at the upper portion of the interior of an outer case 3 and adapted to rotate a drum 5 disposed in the interior of outer case 3 and a heater unit 2 attached to the inner side wall of the outer case and adapted to heat clothing contained in the drum 5. The apparatus also comprises a temperature sensor 6 disposed at the outside of the drum 5 and adapted to sense the internal temperature of the drum 5. At the outer case 3 is disposed a heat exchanging fan 4 which is driven by the driving force of the motor 1 to intake external air into the interior of outer case 3 through an intake opening 10 formed at the outer case 3 and carry out a heat exchange between the air and the high temperature and moist air in the drum 5. At the lower portion of the outer case 3, a dehumidifying passage 9 having a discharge port 11 is provided. Water condensed during the heat exchange is collected at the dehumidifying passage 9 and then discharged through the discharge port 11. Another temperature sensor 7 is disposed in the outer case 3, so as to sense the temperature of an exhaust air, that is, the air completed the heat exchange with the hot and moist air in the drum 5. Within the drum 5, a filter 8 is disposed which serves to filter the air in the drum, so as to separate bits of thread and nap from the air. A door 12 is mounted to the front portion of outer case 3, for giving clothing access to the drum 5.
FIG. 2 is a block diagram of a system for controlling the drying period of the clothing drying apparatus shown in FIG. 1. As shown in FIG. 2, the control system comprises a microcomputer 13 for controlling the operations of the overall system of clothing drying apparatus, depending on the internal temperature of drum 5, the exhaust air temperature and key signals from a key pad 14, a load driving unit 15 including triacs TA1 to TA4 for driving the motor 1 and heater unit 2 under the control of the microcomputer 13, and a display unit 16 for displaying various conditions such as the clothing drying period and etc., under the control of the microcomputer 13. The heater unit 2 comprises three heaters H1 to H3 which are controlled by the triacs TA1 to TA3.
In FIG. 2, the reference character AC denotes an alternating current voltage source.
Now, the operation of the control system for controlling the conventional clothing drying apparatus with the above-mentioned arrangement will be described, in conjunction with FIGS. 3 to 5.
When a wet clothing, for example, a wet blanket is to be dried, the user opens the door 12 and puts the wet blanket into the drum 5. As a blanket key and a drying start key on the key pad 14 are manually pushed, the microcomputer 13 operates to turn on the triac TA4 of the load driving unit 15, thereby causing the motor 1 to be driven. By the driving of motor 1, both the drum 5 and the heat exchanging fan 4 are rotated. On the other hand, the triacs TA1 and TA2 are also turned on by the operation of microcomputer 13, so that the corresponding heater H1 and H2 of the heater unit 2 are actuated. Accordingly, the internal temperature of drum 5 is gradually increased so that the blanket disposed in the drum 5 is gradually dried (a step 1 in FIG. 1).
As air contained in the interior of drum 5 is saturated with a moisture evaporated from the wet blanket, it is changed into a very hot and moist air. This hot and moist air is fed to the heat exchanging fan 4, via the filter 8 mounted to the center portion of the rear portion of drum 5. At the heat exchanging fan 4, the hot and moist air performs a heat exchange with a cold air which is introduced into the interior of outer case 3 through the intake opening 10 by the heat exchange fan 4. Water condensed during the heat exchange is collected at the dehumidifying passage 9 and then discharged out of the dehumidifying passage 9 through the discharge port 11.
By the above-mentioned heat exchange, the dehumidified air is changed into an air which is low in temperature and humidity. The air passes through the dehumidifying passage 9 and is then heated by the heaters H1 and H2. The heated air is then introduced into the drum 5, to dry the blanket disposed in the drum 5.
As shown in FIG. 3, the internal temperature of drum 5 is increased by the operation of heater unit 2, during a predetermined primary drying period t1 after the start of drying. As the evaporation proceeds actively, however, the internal temperature increases no longer and is constantly maintained. When the evaporation is almost completed, the internal temperature of drum 5 increases again. During this primary drying period, the microcomputer 13 determines continuously whether the internal temperature of drum 5 sensed by the temperature sensor 6 has reached a predetermined maximum drying temperature Ta (a step 2 in FIG. 5).
For a maximum drying period of, for example, 5 hours, the microcomputer 13 continues the determination as to whether the sensed internal temperature of drum 5 has reached the predetermined maximum drying temperature Ta (a step 3 in FIG. 5). If the sensed internal temperature of drum 5 has not reached the predetermined maximum drying temperature Ta for the maximum drying period, the microcomputer 13 shut off both the motor 1 and the heater unit 2, thereby causing the drying to cease (a step 4 in FIG. 5). Simultaneously, the microcomputer 13 makes the display unit 16 display an error about the drying.
Where the internal temperature of drum 5 sensed by the temperature sensor 6 has reached the predetermined temperature Ta within the primary drying period t1, the drying rate exceeds 90%. In this case, the microcomputer 13 controls the load driving unit 15, to turn off the heater H2, but to proceed a secondary drying for a secondary drying period t2 (a step 5 in FIG. 5). Such a control of microcomputer 13 is needed for avoiding the blanket in the drum 5 from being maintained at a high temperature for a long time, since the blanket is susceptible to heat.
Thereafter, the microcomputer 13 determines whether the secondary drying period t2 has lapsed (a step 6 in FIG. 5). If the secondary drying period t2 has lapsed, the microcomputer 13 turns off the heater H1 (a step 7 in FIG. 5) and actuates the heat exchange fan 4, so as to proceed a third drying for a third drying period t3 (a step 8 in FIG. 5). After the third drying period t3 has lapsed, the microcomputer 13 shuts off the motor 1 to complete the drying (a step 9 in FIG. 5).
In the above-mentioned conventional clothing drying apparatus, however, there is no consideration about the amount of load, namely, the amount of blankets to be dried, in that the drying operation is continued until the internal temperature of drum sensed by the temperature sensor reaches the predetermined maximum drying temperature. The internal temperature of drum varies depending on the amount of blankets put into the drum, as shown in FIG. 4. Where the amount of blankets is large, the internal temperature of drum may not reach the predetermined maximum drying temperature even after the predetermined maximum period of, for example, 5 hours. In this case, the microcomputer 13 determines such a situation as that the blankets have not been dried yet, ceases the drying and displays an error about it. However, the blankets have already been at a dried condition, even though the internal temperature of drum does not reach the predetermined maximum drying temperature, due to the large amount of blankets in the drum. As a result, the conventional arrangement encounters problems of lengthening the drying period and erroneously determining an actual drying condition of almost 100% as an insufficient drying condition.